Fix infinite prompt loop if status message is printed in prompt

fish will print messages for some jobs when they exit abnormally, such as
with SIGABRT. If a job exits abnormally inside the prompt, then (prior to
this commit) fish would print the message and re-trigger the prompt, which
could result in an infinite loop. This has existed for a very long time.

Fix it by reaping jobs after running the prompt, and NOT triggering a
redraw based on that reaping. We still print the message but the prompt is
not executed.

Add a test.

Fixes #9796

src/reader.rs

@@ -4204,6 +4204,11 @@ impl<'a> Reader<'a> {
         // hack to work.
         reader_write_title(L!(""), zelf.parser, false);
 
+        // Reap jobs but do NOT trigger a repaint.
+        // This is to prevent infinite loops in case a job from the prompt triggers a repaint.
+        // See #9796.
+        job_reap(zelf.parser, true);
+
         // Some prompt may have requested an exit (#8033).
         let exit_current_script = zelf.parser.libdata().exit_current_script;
         zelf.exit_loop_requested |= exit_current_script;

tests/pexpects/prompt_redraw_loop.py

@@ -0,0 +1,30 @@
+#!/usr/bin/env python3
+from pexpect_helper import SpawnedProc
+import re
+
+sp = SpawnedProc()
+send, sendline, sleep, expect_prompt, expect_re, expect_str = (
+    sp.send,
+    sp.sendline,
+    sp.sleep,
+    sp.expect_prompt,
+    sp.expect_re,
+    sp.expect_str,
+)
+expect_prompt()
+
+# Regression test for 9796
+# If a process in the prompt exits with a status that would cause a message to be printed,
+# don't trigger another prompt execution which would result in an infinite loop.
+sendline("sh -c 'kill -ABRT $$'")
+expect_prompt(re.escape("fish: Job 1, 'sh -c 'kill -ABRT $$'' terminated by signal SIGABRT (Abort)"))
+
+# Copy current prompt so we can reuse it.
+sendline("functions --copy fish_prompt fish_prompt_orig")
+expect_prompt()
+
+sendline("function fish_prompt; sh -c 'kill -ABRT $$'; fish_prompt_orig; end")
+expect_prompt(re.escape("fish: Job 1, 'sh -c 'kill -ABRT $$'' terminated by signal SIGABRT (Abort)"))
+
+sendline("echo still alive!")
+expect_prompt("still alive!")